Non-typable (NT) H. influenzae is both a human commensal and a major cause of ear infections. The lipooligosaccharide (LOS) of H. influenzae is a well-documented bacterial component contributing to colonization and diseases. Recently, a study utilizing subtractive hybridization identified a LOS biosynthesis gene (lic2B) as being strongly associated with H. influenzae isolated from the middle ear of children with otitis media and compared to isolates obtained from the nasopharynx of healthy children in daycare. These results suggest that LOS genes may be differentially segregated between NT H. influenzae middle ear and throat isolates. More than sixty genes have been proposed to contribute to the generation of LOS. Many of these synthesize highly variable structures that facilitate survival of H. influenzae in different host environments. Given the complexity of LOS, it is likely that numerous LOS gene differences exist between middle ear and throat isolates. We hypothesize that specific LOS "genotypes" are associated with middle ear isolates. AIM I. Determine the distribution of LOS genes among NT H. influenzae middle ear and throat isolates. AIM II. Identify LOS gene variations and determine their distributions among middle ear and throat isolates.